1. Field of the Invention
The present invention relates to a control apparatus for a hybrid vehicle including an internal combustion engine and a motor and a control method therefor.
2. Description of Related Art
A hybrid vehicle having both an internal combustion engine and a motor for vehicle driving (hereinafter, simply referred to as “vehicle”) has been known. The vehicle has a power dividing mechanism such as a planetary gear train in order to combine a torque generated by the internal combustion engine and a torque generated by the motor to transmit the combined torque to an axle. In order to absorb fluctuation of a torque generated on a crankshaft of the internal combustion engine, a torsional damper in which two shafts provided on both ends are connected via an elastic body (hereinafter, simply referred to as “damper”) is interposed between the internal combustion engine and the power dividing mechanism.
In a vibration suppression apparatus of a drive unit (hybrid drive unit) disclosed in Japanese Patent Application Publication No. 2001-136605 (JP 2001-136605 A), since a torque fluctuation caused by intermittent explosive combustion of an internal combustion engine is transmitted to a motor with a predetermined delay due to elastic deformation of a damper. Accordingly, in order to offset this torque fluctuation, the motor generates a periodically fluctuating torque.
Incidentally, generally a control apparatus of a vehicle selectively performs, based on a driving situation of a vehicle, the residual amount of a battery SOC (State of Charge) and the like, an engine driving mode for driving only by a torque generated by an internal combustion engine, a motor driving mode for driving only by a torque generated by a motor while the internal combustion engine is stopped and a motor assist mode for driving by a torque of both the internal combustion engine and the motor. That is, during the driving of the vehicle, the control apparatus appropriately switches actuation and stopping relating to an operation state of the internal combustion engine.
This control apparatus stops fuel injection when it moves the operation state of the internal combustion engine from actuation to stopping. At this time, in order to avoid vibration and/or occurrence of a noise due to reduction of the rotational speed of the internal combustion engine, the control apparatus needs to set the rotational speed of the internal combustion engine to “0” in a short time. Accordingly, the control apparatus allows the motor to generate “a torque in the direction that stops the rotation of the internal combustion engine” (hereinafter, referred to as “inhibition torque”).
In a vehicle (hybrid vehicle) disclosed in Japanese Patent Application Publication No. 2009-274627 (JP 2009-274627 A), when an internal combustion engine is stopped, a motor generates an inhibition torque. After that, the vehicle performs the control that the speed of reducing the inhibition torque, that is, a change ratio of the inhibition torque is once decreased to prevent the occurrence of shock due to twist of a damper during a process of reducing the inhibition torque.